A method for reducing the content of halogen-containing pollutants in the co-pyrolysis product of wire enamel and polyvinyl chloride

Abstract

This invention discloses a method for reducing the content of halogen-containing pollutants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride, belonging to the field of resource and environmental technology. By adding copper oxide during the co-pyrolysis of enameled wire and polyvinyl chloride, the content of halogen-containing pollutants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride can be significantly reduced, and copper can also be effectively recovered.

Description

Technical Field

[0001] This invention belongs to the field of resource and environmental technology, and in particular relates to a method for reducing the content of halogen-containing pollutants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride. Background Technology

[0002] The enamel coating of waste enameled wire (hereinafter referred to as enameled wire enamel) mainly consists of organic resins such as polyester (PET), polyurethane (PU), and polyesterimide. During the pyrolysis of enameled wire to recover metallic copper, plastic waste such as wires and cables, packaging, rolled strips, and spools are often mixed in, leading to excessive levels of halogen pollutants in the pyrolysis waste. Previous research (patent number CN202210300417.4; paper Li, B.; Wang, X.; Xia, Z.; Zhou, W.; Wu, Y.; Zhu, G. Co-Pyrolysis of Waste Polyester Enameled Wires and Polyvinyl Chloride: Evolved Products and Pyrolysis Mechanism Analysis. J. Anal. Appl. Pyrolysis 2023, 169, 105816. https: / / doi.org / 10.1016 / j.jaap.2022.105816.) has confirmed that co-pyrolysis of enameled wires with common plastic waste polyvinyl chloride (PVC) reduces the emission of organic pollutants in the pyrolysis products to a certain extent compared to the pyrolysis of PVC alone, which is one of the advantages of co-pyrolysis. However, the emission of chlorine-containing pollutants in this method is still relatively high, so new methods for controlling the emission of halogen-containing pollutants need to be developed.

[0003] One of the most commonly used enameled wire enamel materials in production and daily life is polyester, which contains very low levels of halogens. Polyvinyl chloride (PVC), on the other hand, is one of the most common components of plastic waste and a major source of halogens. As a widely used plastic material, PVC is often recycled through pyrolysis. To improve recycling efficiency, thorough dehalogenation is necessary during pyrolysis. Currently, effective dehalogenation methods involve adding dehalogenating agents during pyrolysis. Common dehalogenating agents include alkaline dechlorinating agents and metal oxide dechlorinating agents. It is important to note that in enameled wire recycling, high-value copper is the target material, while polyester enameled wire enamel (EPET) and mixed PVC are waste materials that need to be removed, not recyclable materials. Therefore, due to the different recycling objectives, the enameled wire recycling process conditions, including pyrolysis conditions and the selection of dehalogenating agents, differ from those of ordinary polyester and PVC material recycling processes.

[0004] There are currently no studies on the co-pyrolysis of EPET and PVC with added dehalogenating agents. Summary of the Invention

[0005] One of the main problems with copper recovery from enameled wire pyrolysis is the emission of halogenated pollutants, particularly the high levels of chlorine-containing pollutants caused by the mixing of waste materials containing high PVC content into the recycled waste enameled wire. Regarding the issue of chlorine-containing pollutant emissions, existing production and research efforts largely focus on controlling chlorine-containing pyrolysis products for the purpose of PVC recovery, while research on the use of dehalogenating agents and pyrolysis processes in the co-pyrolysis of enameled wire and PVC, with the ultimate goal of recovering Cu materials, is lacking. Therefore, this invention proposes a method to reduce the halogenated pollutant content in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride (PVC). This method effectively controls pollutant emissions, especially chlorine-containing pollutants, during the co-pyrolysis of enameled wire and PVC plastic by adding a dehalogenating agent (copper oxide).

[0006] To achieve the above objectives, this invention provides a method for reducing the content of halogenated contaminants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride (PVC). Copper oxide is added during the co-pyrolysis of enameled wire and PVC. The copper oxide acts as a dehalogenating agent, reducing the content of halogenated contaminants in the co-pyrolysis products of enameled wire enamel and PVC.

[0007] Furthermore, the copper oxide is either copper oxide (CuO) or cuprous oxide (Cu2O), both of which can absorb the hydrochloric acid gas produced by the decomposition of PVC to generate solid copper chloride, thus achieving a chlorination effect.

[0008] Furthermore, the copper oxide is CuO.

[0009] Furthermore, the enameled wire enamel is polyester enameled wire enamel (EPET).

[0010] Furthermore, the mass ratio of enameled wire enamel, polyvinyl chloride and copper oxide is 9:1:(1-3).

[0011] Furthermore, the mass ratio of enameled wire enamel, polyvinyl chloride, and copper oxide is 9:1:3.

[0012] Furthermore, the co-pyrolysis temperature is 200-800℃.

[0013] Furthermore, the co-pyrolysis temperature is 240-640℃.

[0014] Another aspect of this invention is the recovery of metallic copper (Cu) from enameled wire, and the reduction of halogenated contaminant content in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride (PVC). Therefore, to avoid the introduction of unnecessary metallic impurities, copper oxide is added as a dehalogenating agent. CuO can reduce the generation of benzene, toluene, indene, naphthalene, anthracene, and other compounds in PVC pyrolysis products, while simultaneously reducing the total emission of chlorine-containing contaminants. Furthermore, the chlorine emission also depends on the ratio of PVC to CuO; when the mass ratio is 1:3, the Cl released by the PVC-CuO system is 6.2% of the total PVC content. Simultaneously, increasing the mass ratio of CuO to PVC can effectively inhibit the formation of dioxins. Moreover, the main dehalogenation mechanism of CuO is believed to be the reaction of CuO with hydrochloric acid (HCl), the main product of PVC pyrolysis, to generate copper chloride (CuCl2), achieving chlorine fixation, that is, retaining more Cl in solid inorganic matter, thus reducing its content in gaseous and liquid pyrolysis products. Therefore, based on the above research results, CuO can theoretically be used as a dechlorinating agent in the co-pyrolysis of EPET and PVC.

[0015] This invention focuses on the study and analysis of the effects of CuO on the pyrolysis of EPET, PVC, and their co-mixtures. The main research methods employed include thermogravimetric analysis (TG and DTG) to study pyrolysis conditions such as pyrolysis temperature, Py-GC / MS to study the pyrolysis organic products, and ion chromatography to detect the chlorine content in the pyrolysis gas. The chloride ion content of the solid residue after pyrolysis was determined by Eschka mixture fusion-potassium bisulfate titration. Through these studies, the process flow and conditions for controlling pollutants in the co-pyrolysis of CuO with EPET and PVC were obtained, as well as the distribution of chlorine-containing pollutants in the gas, liquid (oil), and solid phases of the pyrolysis products. This provides a method for reducing pollutant emissions and offers methodological and theoretical guidance for the industrial production of enameled wire pyrolysis.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects:

[0017] The TG-DTG curves reveal the single and blended pyrolysis temperature ranges of EPET, PVC, and dehalogenator CuO, demonstrating the influence of CuO on the co-pyrolysis process and degree of pyrolysis. Furthermore, this invention employs Py-GC / MS to characterize the specific components and contents of the pyrolysis products of single and blended materials, clearly identifying the composition of the pyrolysis oil, including the types, components, and contents of chlorine-containing pollutants. This information can be used to determine the effectiveness of pollutant emission control in pyrolysis oil (liquid phase) under different conditions. Simultaneously, this invention collects the gaseous products and solid residues from pyrolysis and uses ion chromatography and the Eschka mixture method, respectively, to determine the chlorine content in the pyrolysis gas and solid residues. This information is used to assess the effectiveness of pollutant emission control in gaseous and solid pyrolysis products under different conditions. Through these methods, this invention obtains the optimal co-pyrolysis process, clarifies the dechlorination mechanism of co-pyrolysis, and achieves the goal of minimizing the emission of chlorine-containing pollutants from pyrolysis products. Attached Figure Description

[0018] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 This is a schematic diagram of a pyrolysis and gas collection device;

[0020] Figure 2 The thermogravimetric curves of 1PVC-3CuO in Example 1 are shown, where (a) is the TG curve and (b) is the DTG curve.

[0021] Figure 3 The thermogravimetric curves of 3EPET-1CuO in Example 2 are shown, where (a) is the TG curve and (b) is the DTG curve.

[0022] Figure 4 The thermogravimetric curves of 9EPET-1PVC-3CuO in Example 3 are shown, where (a) is the TG curve and (b) is the DTG curve.

[0023] Figure 5 This is a linear regression equation for chloride ion concentration and peak area;

[0024] Figure 6 The thermogravimetric curves of PVC in Example 1 are shown, where (a) is the TG curve and (b) is the DTG curve.

[0025] Figure 7 The mechanism of chlorine-containing pollutant generation from the pyrolysis of PVC, EPET-PVC, and EPET-PVC-CuO. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] In an embodiment of the present invention, a tubular furnace is used to pyrolyze PVC, PVC-CuO, EPET-PVC, and EPET-PVC-CuO, and the pyrolysis gas is collected. An ion chromatograph is used to detect the chlorine content in the pyrolysis gas. A schematic diagram of the pyrolysis and gas collection device is shown below. Figure 1As shown, the gas collection device consists of four 500mL gas collecting bottles, a right-angle glass tube, a rubber tube, and a tail gas absorption bottle. Bottle ① is empty and its main function is to cool the organic oil and prevent backflow; bottles ② and ③ collect chlorine-containing gas, each containing 250mL of liquid; bottle ④ is empty and its main function is to prevent backflow; bottle ⑤ is a tail gas absorption bottle containing anhydrous ethanol. The collecting liquid is a 0.1mol / L NaOH solution prepared from analytical grade NaOH and deionized water. After pyrolysis, the liquids from bottles ② and ③ are mixed and stirred for 15 minutes using a magnetic stirrer. 10mL of the liquid is then taken for ion chromatography analysis. The ion chromatography eluent is prepared as follows: analytical grade NaHCO3 and Na2CO3 are mixed with ultrapure water with a resistivity of 18.2MΩ to prepare a mixed eluent with concentrations of 1.8mM NaHCO3 and 1.7mM Na2CO3.

[0032] Solid residues after pyrolysis in each embodiment were sampled, and their chloride ion content was determined by the Eschka mixture fusion-potassium bisulfate titration method, referring to GB / T 3558-2014. The key steps are as follows: After pyrolysis, the sample was ground and mixed with the Eschka mixture, then melted in a muffle furnace to convert chloride into chloride. The chloride was extracted with boiling water, and excess silver nitrate solution was added in an acidic medium. Using ammonium ferric sulfate as an indicator, titration was performed with potassium bisulfate, and the chloride content in the solid residue was calculated based on the actual amount of silver nitrate consumed. The Eschka mixture used was a mixture of magnesium oxide and anhydrous sodium carbonate in a mass ratio of 2:1.

[0033] Example 1

[0034] PVC and CuO were mixed in an Al2O3 crucible (the mass ratio of PVC to CuO was 1:3, and the total mass was 10.000±0.300 mg). The crucible was placed in a tube furnace for pyrolysis under a N2 atmosphere at a flow rate of 50 mL / min. The temperature was increased from 30 °C to 800 °C at a rate of 10 °C / min. This mixture was denoted as 1PVC-3CuO.

[0035] The effect of CuO on the thermogravimetric behavior of PVC was investigated. The thermogravimetric curve of 1PVC-3CuO in Example 1 is shown below. Figure 2 (a) TG curve, (b) DTG curve; the thermogravimetric curve of PVC in Example 1 is shown in [reference needed]. Figure 6The graphs (a) and (b) show the TG curves. It can be seen that the TG / DTG curves of 1PVC-3CuO after the addition of CuO are significantly different from those of pure PVC. The DTG curve of 1PVC-3CuO indicates that its pyrolysis has four stages, two more than that of pure PVC. The first stage of pyrolysis of 1PVC-3CuO is from 238 to 313℃, with a peak temperature and rate of 283℃ and 2.86% / min, respectively. The second stage is from 313 to 401℃, with a peak temperature and rate of 367℃ and 1.59% / min, respectively. The third stage is from 401 to 540℃, with a peak temperature and rate of 494℃ and 1.47% / min, respectively. The fourth stage is from 540 to 692℃, with a peak temperature and rate of 637℃ and 3.3% / min, respectively. Unlike PVC pyrolysis, the weight loss in the first and second stages of the 1PVC-3CuO pyrolysis was 5.48% and 3.45%, respectively, while the weight loss in the third and fourth stages was 13.18% and 28.96%, respectively. This is likely because CuO reacts with HCl produced during PVC pyrolysis in the first and second stages, reducing its thermal weight loss. Simultaneously, since HCl produced during PVC pyrolysis has an autocatalytic effect on its own pyrolysis, the reduction in HCl lowers the overall PVC pyrolysis rate, delaying the PVC pyrolysis termination temperature by approximately 150°C. Analyzing the weight loss rate, for a PVC to CuO mass ratio of 1:3, the theoretical weight loss would be 25% if only PVC were pyrolyzed, but the measured weight loss rate reached 51%, indicating that oxygen in CuO also participated in the reaction, leading to the increased weight loss rate.

[0036] Example 2

[0037] EPET and CuO were mixed in an Al2O3 crucible (the mass ratio of EPET to CuO was 3:1, and the total mass was 10.000±0.300 mg). The crucible was placed in a tube furnace for pyrolysis under a N2 atmosphere at a flow rate of 50 mL / min. The temperature was increased from 30 °C to 800 °C at a rate of 10 °C / min. This mixture was denoted as 3EPET-1CuO.

[0038] The effect of CuO on the thermogravimetric behavior of EPET was studied, and the experimental results are as follows: Figure 3 As shown, the pyrolysis process of 3EPET-1CuO is similar to that of EPET, with only one pyrolysis stage. Its pyrolysis initiation temperature is 292℃, and its pyrolysis termination temperature is 482℃. The peak temperature and rate of thermogravimetric loss are 409℃ and 6.21% / min, respectively, with a weight loss rate of 42.6%. The comparison of characteristic parameters shows that the pyrolysis characteristics of EPET did not change significantly after the addition of CuO, indicating that the introduction of CuO has no significant impact on the pyrolysis parameters of EPET.

[0039] Example 3

[0040] EPET, PVC and CuO were mixed in an Al2O3 crucible (the mass ratio of EPET, PVC and CuO was 9:1:3, and the total mass was 10.000±0.300mg). The crucible was placed in a tube furnace for pyrolysis under a N2 atmosphere at a flow rate of 50mL / min. The temperature was increased from 30℃ to 800℃ at a rate of 10℃ / min. This mixture was denoted as 9EPET-1PVC-3CuO.

[0041] The effect of CuO on the thermogravimetric behavior of 9EPET-1PVC was studied, and the experimental results are as follows: Figure 4 As shown, the pyrolysis of 9EPET-1PVC-3CuO can be divided into three stages, one more than that of 9EPET-1PVC. The first stage of pyrolysis for 9EPET-1PVC-3CuO is from 242 to 328℃, with a peak thermogravimetric loss temperature and rate of 279℃ and 1.14% / min, respectively. The second stage is from 328 to 439℃, with a peak thermogravimetric loss temperature and rate of 392℃ and 5.85% / min, respectively. The third stage is from 439 to 636℃, with a peak thermogravimetric loss temperature and rate of 554℃ and 1.59% / min, respectively. The pyrolysis termination temperature of 9EPET-1PVC-3CuO is delayed by approximately 100℃ compared to 9EPET-1PVC. The appearance of the third stage of pyrolysis is caused by CuO, and its mechanism is roughly the same as the effect of CuO on PVC. Meanwhile, the pyrolysis termination temperature of 9EPET-1PVC-3CuO is about 50°C lower than that of 1PVC-3CuO. This may be because the benzoic acid produced by the pyrolysis of EPET promotes the pyrolysis of PVC, thereby causing its pyrolysis termination temperature to be earlier.

[0042] Example 4

[0043] EPET, PVC and CuO were mixed in an Al2O3 crucible (the mass ratio of EPET, PVC and CuO was 9:1:3, and the total mass was 10.000±0.300mg). The crucible was placed in a tube furnace for pyrolysis under a N2 atmosphere at a flow rate of 50mL / min. The temperature was increased from 30℃ to 800℃ at a rate of 10℃ / min. This mixture was denoted as 9EPET-1PVC-1CuO.

[0044] The pyrolysis products of 9EPET-1PVC-1CuO and 9EPET-1PVC-3CuO were analyzed using Py-GC / MS. This method involves connecting a gas chromatograph / mass spectrometer externally to a tubular furnace for rapid pyrolysis of the experimental samples and analysis of the products. Based on the thermogravimetric parameters obtained in Example 3, the temperature points were set to 440℃ and 640℃, respectively. The instrument was preheated to the specified temperatures, and then the samples were placed in the furnace for pyrolysis for 12 seconds. Volatile water vapor was separated using an Agilent UA-5MS capillary column (30m*0.25mm*0.25mm). The gas chromatographic column oven temperature programming was as follows: the instrument first increased the temperature from 40℃ to 80℃ at a rate of 5℃ / min, then increased it to 300℃ at a rate of 15℃ / min; the GC injection port temperature was 320℃; the split ratio was 30; and the column flow rate was 1mL / min. The electron energy in the mass spectrometer (MS) was 70 eV, the ion source temperature was 230℃, the transfer line temperature was 300℃, the mass scan range was 40-550 m / z, and the scan mode was full scan. High-purity He (99.999%) was used as the carrier gas for gas chromatography / mass spectrometry, and the flow rate was kept constant at 1 mL / min. The obtained pyrolysis main products and their contents are shown in Table 1. The pyrolysis products of 9EPET-1PVC-1CuO at 440℃ were mainly benzoic acid, 1,2-ethylene glycol dibenzoate, acrylone, and vinyl formate, while the main products at 640℃ were benzoic acid, 1,2-ethylene glycol dibenzoate, benzene, ethylamine, acrylone, vinyl formate, biphenyl, etc., including acids, esters, ketones, hydrocarbons, and alcohols, accounting for 80.55 wt.% of the total products. Benzoic acid accounted for 48.27 wt.% of the total product content, and 1,2-ethylene glycol dibenzoate accounted for 10.24 wt.%. Compared with 440℃, the contents of benzoic acid, benzene, biphenyl, and vinyl benzoate increased during pyrolysis at 640℃, while the contents of other substances decreased. This is because as the temperature increases, the pyrolysis products tend to become smaller molecules, i.e., their structures become simpler. Additionally, 4.60 wt.% ethylamine appeared in the product at 640℃. The nitrogen element in this product may have originated from additives in the enameled wire. Elemental analysis of 9EPET-1PVC using an organic elemental analyzer revealed a carbon content of 36.9 wt.%, a hydrogen content of 2.85 wt.%, and a nitrogen content of 0.46 wt.%.

[0045] Table 1. Pyrolysis products of 9EPET-1PVC-1 with CuO content greater than 1 wt.%.

[0046]

[0047] Table 2 shows the chlorinated organic compounds generated during the pyrolysis of 9EPET-1PVC-3CuO. The types of chlorinated organic compounds generated during the pyrolysis of 9EPET-1PVC-3CuO are more numerous than those generated during 9EPET-1PVC, but their content is less. The total content of chlorinated organic compounds generated during the pyrolysis of 9EPET-1PVC-3CuO at 440℃ accounts for 2.54% of the total product content. The main chlorinated organic compounds are 2-chlorobenzoic acid-2-oxo-2-phenylethyl ester chloride (0.96 wt.%), 2-chlorobenzoic acid (0.54 wt.%), and 2,5-dichlorobenzoic acid (0.37 wt.%). As the temperature increases, the content of chlorinated organic compounds increases. At 660℃, the chlorinated organic compounds produced by pyrolysis account for 3.35 wt.% of the total product, with chlorobenzene (0.91 wt.%), 4-chlorobenzoyl chloride (0.32 wt.%), di(2-chloroethyl) terephthalate (0.38 wt.%), and 2-chlorobenzoic acid-2-oxo-2-phenylethyl ester (0.62 wt.%) being the main chlorinated organic compounds. In terms of species, the chlorinated organic compounds produced by the pyrolysis of 9EPET-1PVC-3CuO are mainly chlorinated aromatic hydrocarbons, accounting for 1.25 wt.% of the total product. This differs from the types of chlorinated organic compounds produced by the pyrolysis of 9EPET-1PVC (whose main product is vinyl chloride esters). It was also found that, apart from chlorinated aromatic hydrocarbons, the chlorine atom in other chlorinated aromatic compounds is often directly attached to the benzene ring, such as 2-chlorobenzoic acid-2-oxo-2-phenylethyl ester (0.62 wt.%) and 3,4-dichlorodiphenyl ethyl ketone (0.12 wt.%), and the variety of these compounds increases with increasing temperature.

[0048] The above experimental results indicate that the addition of CuO causes the chlorinated organic compounds produced by the pyrolysis of 9EPET-1PVC to change from chlorinated esters to chlorinated aromatic hydrocarbons and their derivatives. The mechanism is believed to be that CuO reacts with HCl to generate CuCl2 or CuCl, which reduces the HCl content, weakens the secondary reaction of HCl with other co-pyrolysis products, and reduces the generation of chlorinated organic compounds.

[0049] Table 2. Chlorinated organic compounds (wt.%) generated during the pyrolysis of 9EPET-1PVC-3CuO

[0050]

[0051]

[0052] The chlorine content in the pyrolysis oil is represented by chlorinated organic compounds. Based on the Py-GCMS analysis above, where the temperature used was the pyrolysis termination temperature of the sample, the results are shown in Table 3. It can be seen that the chlorinated organic compounds generated from 9EPET-1PVC account for 12% of the total products, while those generated from 9EPET-1PVC-3CuO account for 3%. That is, CuO reduces the chlorinated organic compounds generated from the pyrolysis of 9EPET-1PVC from 12% to 3%. The chlorinated organic compounds generated from the pyrolysis of 9EPET-1PVC are the result of the reaction between the EPET pyrolysis products and HCl. When CuO absorbs the HCl, the chlorinated organic compounds in the pyrolysis oil decrease. The results of this example fully demonstrate that CuO, as a dehalogenating agent, can significantly reduce the emission of chlorine-containing pollutants in the liquid phase products of co-pyrolysis.

[0053] Table 3. Chlorinated organic matter content in pyrolysis oil

[0054]

[0055] The chlorine content in the pyrolysis gases of different samples from Examples 1-4 was determined using ion chromatography. Pyrolysis was first carried out in a closed tubular furnace, and the heating process of the furnace was controlled by a programmable controller. A schematic diagram of the sample pyrolysis and gas collection device is shown below. Figure 1 As shown. A small amount of sample was placed in an alumina (Al2O3) crucible and then placed in a tube furnace. Nitrogen gas was pre-purged at a rate of 0.5 L / min for 10 min, and then the protective gas flow rate was adjusted to 0.1 L / min. The tube furnace was set to heat to 800 °C at a rate of 10 °C / min for pyrolysis. After pyrolysis, the liquids in bottles ② and ③ were mixed and stirred for 15 min using a magnetic stirrer. 10 mL of the liquid was then taken for ion chromatography analysis. The specific test steps are as follows.

[0056] Chloride ion concentration determination in ion chromatography standard solutions. Standard solutions with sample concentrations of 0.00005, 0.00025, 0.0005, 0.0025, and 0.005 mol / L were measured using an ion chromatograph. The chloride ion peak area was obtained from the peak height in the chromatogram, and the results are shown in Table 4.

[0057] Table 4. Peak areas corresponding to the concentrations of ion chromatography standard solutions.

[0058]

[0059] A linear regression curve was obtained by linearly fitting the chloride ion concentration and peak area data, as shown in [the figure]. Figure 5 .from Figure 5 The following linear regression equation (1) was obtained. The correlation coefficient of the linear regression equation reached 0.9989, indicating that the fitting curve has high reliability.

[0060] ya =11198x c -0.545 (1)

[0061] Where, x c Chloride ion concentration; t a The peak area is denoted as .

[0062] The pyrolysis gases of four samples—PVC, 1PVC-3CuO, 9EPET-1PVC, and 9EPET-1PVC-3CuO—were analyzed by ion chromatography to detect chloride ions. The chloride ion content w was calculated using equation (2). t .

[0063]

[0064] In equation (2), w t denoted as ν; c is the chloride ion content; ν is the chloride ion concentration in the collected liquid, in mol / L; V is the volume of the collected liquid, in L; M is the relative atomic mass of chlorine; m is the total mass of chlorine.

[0065] The calculated chloride ion content in the pyrolysis gas of the four samples is shown in Table 5. Table 5 shows that the chloride ion content in the gas was highest when PVC was pyrolyzed alone, at 54%. When CuO and PVC were co-pyrolyzed, the chloride ion content in the gas decreased significantly to only 14%, a reduction of 40%. This indicates that the HCl released during the pyrolysis of CuO and PVC reacted. When EPET and PVC were co-pyrolyzed, the chloride ion content also decreased, accounting for 24% of the total chloride content, a 30% reduction compared to PVC. EPET also consumes the HCl produced during PVC pyrolysis, resulting in a decrease in the chloride ion content in the pyrolysis gas. When EPET, PVC, and CuO were co-pyrolyzed, the chloride ion content in the pyrolysis gas was the lowest, accounting for only 7% of the total chloride mass. In all four samples, the source of chloride was PVC pyrolysis, which produces a large amount of HCl gas. The reason for the decrease in chloride ions in the pyrolysis gas is the reaction between CuO / EPET and HCl. The HCl released during the thermal decomposition of PVC reacts with CuO to form CuCl2 or CuCl. The products of the thermal decomposition of EPET, such as vinyl benzoate or ethyl benzoate, undergo addition or acid hydrolysis reactions with HCl, resulting in a reduction in the amount of HCl released and a decrease in the chloride ion concentration in the collected solution.

[0066] Table 5 Chloride ion content in pyrolysis gases

[0067]

[0068] Chloride ion content was determined by Eschka titration of the pyrolysis solid residues of 9EPET-1PVC and 9EPET-1PVC-3CuO. Pyrolysis was first carried out in a closed tube furnace, with the heating process controlled by a programmable controller. A small amount of sample was placed in an alumina (Al2O3) crucible and then loaded into the tube furnace. Nitrogen gas was pre-purged at a rate of 0.5 L / min for 10 min, and then the protective gas flow rate was adjusted to 0.1 L / min. The tube furnace was set to heat to the preset temperature at a rate of 10 °C / min for pyrolysis. The pyrolysis solid residues were ground and then titrated with Eschka to determine their chloride content. Reagent preparation is described in step (4), and detailed experimental parameters are shown in Table 6. Based on the experimental parameters obtained in Table 6, the chloride ion concentration c in the pyrolysis solid residues was calculated using equation (3). cl The results are listed in Table 6.

[0069]

[0070] In equation (3), c cl V1 is the chloride ion concentration; V1 is the sample volume; c is the concentration of potassium thiocyanate standard solution, in mmol / mL; M cl is the relative atomic mass of chlorine; m is the total mass of chlorine.

[0071] Table 6 Chloride ion content in pyrolysis solid residues

[0072]

[0073] The chlorine content (w) in the solid residue relative to the total chlorine content of the sample was calculated according to equation (4). Cl The results are shown in Table 7. Table 7 shows that 1PVC-3CuO, 9EPET-1PVC, and 9EPET-1PVC-3CuO, at the pyrolysis completion temperature, w Cl The concentrations were 7.39%, 5.75%, and 19.7%, respectively. At the end of the pyrolysis, the chlorine content in the 9EPET-1PVC-CuO solid residue was the highest, indicating that CuO has a good chlorine-fixing effect. This also shows that when EPET and CuO are present simultaneously, their dechlorination effect on the pyrolysis gas is the best, followed by CuO; EPET also has a certain dechlorination effect.

[0074]

[0075] In equation (4), w Cl ρ represents the chlorine content in the solid residue as a percentage of the total chlorine in the sample; m represents the total mass of chlorine; c represents the total mass of chlorine. cl This represents the chloride ion concentration.

[0076] Table 7. Chlorine content in pyrolysis solid residue as a percentage of chlorine content in PVC.

[0077]

[0078] Based on the above research results, this invention summarizes the formation mechanisms of major chlorine-containing pollutants from the single and blended pyrolysis of PVC, EPET, and CuO, such as... Figure 7 As shown. When PVC is pyrolyzed alone, it releases large amounts of HCl, chlorinated alkanes, and chlorinated aromatics (left). When PVC and EPET are co-pyrolyzed, HCl reacts with vinyl esters in the EPET pyrolysis products to form chlorinated esters, reducing the release of acidic HCl gas and decreasing the content of chlorinated alkanes (middle). When EPET, PVC, and CuO are co-pyrolyzed (right), CuO reacts with HCl to form copper chloride, achieving a chlorine-fixing effect and significantly reducing the HCl content. Therefore, the formation of chlorinated esters is reduced, while the proportion of chlorinated aromatics in the products increases, but the total emission of chlorine-containing pollutants is significantly reduced.

[0079] Based on the above embodiments, the present invention arrives at the following important conclusions:

[0080] (1) CuO has different effects on the pyrolysis behavior and products of EPET, PVC, and their blends. CuO has little effect on the pyrolysis characteristics of EPET, but it increases the number of pyrolysis stages of PVC to four and delays the pyrolysis termination temperature by nearly 150°C; it also increases the number of pyrolysis stages of 9EPET-1PVC and delays the pyrolysis termination temperature by nearly 100°C. The total amount of chlorinated organic compounds produced by the pyrolysis of 9EPET-1PVC-3CuO is reduced, and the main types are chlorinated aromatic hydrocarbons and their derivatives, thereby reducing the toxicity of the chlorinated organic compounds produced by the pyrolysis of 9EPET-1PVC.

[0081] (2) The mechanism by which CuO affects the pyrolysis of 9EPET-1PVC is its chlorine-fixing effect. During the pyrolysis process, the HCl released by PVC is absorbed by CuO, reducing the effect of HCl on the dehydrochlorination of tertiary chlorides, reducing the formation of benzene, and further delaying the release of HCl. This weakens the catalytic effect of HCl on PVC pyrolysis, leading to an increase in the types and a decrease in the total amount of chlorinated aromatic hydrocarbons and their derivatives. At the same time, due to the effect of CuO, the interaction between HCl and EPET pyrolysis products is reduced, resulting in a decrease in chlorinated esters and acyl chlorides in chlorinated organic compounds.

[0082] (3) CuO reduces the chlorine content in the gas and oil (liquid phase) during the pyrolysis of 9EPET-1PVC, and increases the content of inorganic chlorides in the solid. Therefore, the chlorine fixation effect is best when EPET and CuO are present at the same time, and the emission of chlorine-containing pollutants is significantly reduced.

[0083] In summary, introducing the dehalogenating agent CuO into the co-pyrolysis system of EPET and PVC can significantly reduce the emission of chlorine-containing pollutants in the pyrolysis products.

[0084] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for reducing the content of halogenated contaminants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride, characterized in that, Copper oxides are added during the co-pyrolysis of enameled wire and polyvinyl chloride; The oxide of copper is copper oxide; The mass ratio of enameled wire enamel, polyvinyl chloride and copper oxide is 9:1:(1-3); The co-pyrolysis temperature is 240-640℃.

2. The method for reducing the content of halogenated contaminants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride according to claim 1, characterized in that, The enameled wire enamel is a polyester enameled wire enamel.

3. The method for reducing the content of halogenated contaminants in the co-pyrolysis products of enameled wire enamel and polyvinyl chloride according to claim 1, characterized in that, The mass ratio of enameled wire enamel, polyvinyl chloride and copper oxide is 9:1:3.

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